1. Field of the Invention
The present invention relates to a vibration detecting apparatus for use in the detection of vibration of an equipment subject to vibration of a relatively low frequency for example in a range from 1 to 30 Hz, and more particularly to a vibration detecting apparatus adapted to be loaded in an equipment such as camera and enabling to precisely and rapidly detect the vibration of said frequency range in said equipment.
2. Related Background Art
For detecting vibration, for example caused by hand shaking in a camera, it has been proposed, for example in the British Patent No. 2116397A, to install a vibration detecting apparatus incorporating an acceleration meter in the camera and to integrate the output of said acceleration meter indicating the acceleration once or twice with an integrating circuit to obtain the speed or the displacement by vibration.
FIG. 40 schematically shows a conventional method and apparatus for detecting the displacement of a camera caused by vibration. Such conventional method and apparatus for detecting camera vibrations have been associated with the following drawbacks.
Reference is made to FIGS. 40 to 43 in the following explanation of said drawbacks.
FIG. 40 illustrates a system for detecting the vertical vibration of the camera in a direction 4, and the system for detecting the lateral vibration perpendicular to the plane of drawing is omitted. In FIG. 40, there are shown a camera body 1; a camera lens 2; and two acceleration meters 3a, 3b such as servo acceleration meters, capable of detecting a small amount of acceleration respectively in directions 3a', 3b'. Similar acceleration meters can be used for detecting lateral vibration of the camera, and, in such case the acceleration is detected in directions which are 90.degree. to the directions 3a', 3b', namely perpendicular to the plane of drawing.
There are also provided a differential amplifier 5 for obtaining the difference of outputs of the two acceleration meters 3a, 3b and an integrating circuit 6. Said integrating circuit 6 has a two-stage structure as shown in FIG. 41, in which the first stage converts the output of the differential amplifier, indicating the acceleration, into the speed, and the second stage converts the speed into the displacement, thus releasing a displacement signal 7.
In the unit (a) or (b) in FIG. 41, there are provided an operational amplifier 8; a resistor 9; and a capacitor 10. An input terminal 11 receives the output of the differential amplifier 5, and an output terminal 12 releases a speed signal, while an output terminal 13 releases a displacement signal. In the integrating circuits of the first and second stages, the resistors 9 or the capacitors need not be mutually equal but can be suitably selected in order to obtain a high precision in the output in rapid manner.
A reset switch 14, when closed, short-circuits the capacitor 10 to interrupt the function of the integrating circuit, and, when opened, starts the integration by charging the capacitor 10.
Now reference is made again to FIG. 40, for explaining the vibration detecting operation. Let us consider a situation where the operator aims the camera at an object. In this state the camera causes small vibrations in the direction 4 and in the direction perpendicular to the plane of drawing. This vibration is principally a motion of acceleration, having a frequency in a range of 1 to 30 Hz. In FIG. 40, a camera vibration in the direction 4 gives different accelerations to the acceleration meters 3a, 3b. This is because, in case of a vibration around a point O, the acceleration is larger in the acceleration meter 3a which is farther from the point O than in the acceleration meter 3b which is closer to the point O. An acceleration signal representing the vertical vibration of the camera in the direction 4 can be obtained by determining the difference of the outputs of two acceleration meters 3a, 3b by means of the differential amplifier 5, and the vibrational displacement of the camera can be detected by integrating the output of said differential amplifier 5 by means of two-stage integrating circuit 6.
FIGS. 42A, and 42B illustrate the wave form of the acceleration signal and that of the speed signal obtained by integrating said acceleration signal, in the conventional vibration detecting apparatus as explained above. More specifically, FIG. 42A shows the ideal wave form, in the first-stage integrating circuit shown in FIG. 41(a), of the speed signal 16 at the output terminal 12 obtained by integrating the acceleration signal 15 received at the input terminal 11. In practice, however, because of the fluctuation in the precision of the acceleration meters 3a, 3b, the difference of the outputs of said acceleration meters from the differential amplifier 5 contains, as shown by the acceleration signal 15.sub.1 in FIG. 42B, a certain bias 20.sub.1, displaced from the zero point (indicated by arrow 19) of said acceleration signal. The integration of such acceleration signal 15.sub.1 will inevitably involve the integration of the above-mentioned bias, so that the accuracy of the speed signal 16.sub.1 after integration becomes significantly deteriorated as shown in FIG. 42B.
Consequently it has been proposed, as shown in FIG. 43, to serially connect a high-pass filter 21, shown in FIG. 44, between the differential amplifier 5 and the integrator 6, thereby removing the output of a very low frequency, for example less than 1 Hz, thus eliminating the bias component in the input signal to the integrator.
As shown in FIG. 44, said high-pass filter is composed of an input terminal 11 for receiving the acceleration signal containing a bias signal composed of a DC component and a low frequency component of a frequency less than 1 Hz; an RC serial circuit consisting of a resistor 9 and a capacitor 10 for cutting off the bias component; an RC parallel circuit consisting of a resistor 9 and a capacitor 10 for eliminating noises and determining the degree of amplification; an operational amplifier 8; and an output terminal 22 releasing the acceleration signal free from the bias component. Consequently the differential acceleration signal received at the input terminal 11 is subjected to the removal of the bias component in the high-pass filter 21, and is released as a corrected acceleration signal.
FIG. 45 shows the function of the high-pass filter 21. The acceleration signal 15.sub.1 supplied to the input terminal 11 contains a bias component 20.sub.1. By passing such input signal through the high-pass filter 21, there is obtained in the output terminal the corrected acceleration signal 15.sub.2 not containing the bias component.
However, as will be apparent from FIG. 45 showing the signal wave form, the corrected acceleration signal 15.sub.2 enters a stable area of elimination of the bias component at a time B after the lapse of a period .tau. from the start A of the input to the high-pass filter 21, and said stabilizing period .tau. is proportional to the product of the resistance and the capacitance of the RC serial circuit determining the high-pass time constant. In order to precisely detect the low frequency vibration of 1 to 30 Hz as in the camera vibration caused by hand shaking by completely removing the bias component, it is necessary to select a considerably large high-pass time constant, so that the above-mentioned period .tau. inevitably becomes considerably long.
Also the integrating circuit requires a very long time for restoring a normal operation once it is saturated by some reason. It is therefore known that the integrating circuit may require a stabilizing time as in the high-pass filter.
In the actual camera operation, such saturation of the integrating circuit tends to occur in photographing continuous pictures or panorama pictures. More specifically, the probability of saturation of the integrating circuit becomes very high when the camera is swung, after aimed at a first object, to another second object.
The presence of such waiting time for stabilizing the output in the high-pass filter and in the integrating circuit is heavily detrimental in the practical use.